I. Field of the Invention
The present invention relates generally to the modification and control of the temperature of the body. More particularly, the invention relates to a method for controlling body temperature by irrigating the bladder with a working fluid.
II. Description of the Related Art
Organs in the human body, such as the brain, kidney and heart, are maintained at a constant temperature of approximately 37xc2x0 C. Hypothermia can be clinically defined as a core body temperature of 35xc2x0 C. or less. Hypothermia is sometimes characterized further according to its severity. A body core temperature in the range of 33xc2x0 C. to 35xc2x0 C. is described as mild hypothermia. A body temperature of 28xc2x0 C. to 32xc2x0 C. is described as moderate hypothermia. A body core temperature in the range of 24xc2x0 C. to 28xc2x0 C. is described as severe hypothermia.
Patients may require pre or post-operative cooling for a variety of reasons, including, for example, treatment of a malignant hypothermia crisis and induction of therapeutic hypothermia for neurosurgery.
Catheters have been developed which are inserted into the bloodstream of the patient in order to induce total body hypothermia. For example, U.S. Pat. No. 3,425,419 to Dato describes a method and apparatus of lowering and raising the temperature of the human body. The Dato invention is directed towards a method of inducing moderate hypothermia in a patient using a metallic catheter. The metallic catheter has an inner passageway through which a fluid, such as water, can be circulated. The catheter is inserted through the femoral vein and then through the inferior vena cava as far as the right atrium and the superior vena cava. The Dato catheter has an elongated cylindrical shape and is constructed from stainless steel.
Other less cumbersome catheters have been developed to provide cooling intravascularly. For example, a heat transfer element such as disclosed in U.S. Pat. No. 6,096,068, incorporated herein by reference in its entirety, may be placed in the feeding artery of an organ to absorb or deliver the heat from or to the blood flowing into the organ. The transfer of heat may cause either a cooling or a heating of the selected organ. The heat transfer element is small enough to fit within the feeding artery while still allowing a sufficient blood flow to reach the organ in order to avoid ischemic organ damage. By placing the heat transfer element within the feeding artery of an organ, the temperature of the organ can be controlled with less of an effect on the temperature of the remaining parts of the body. A similar heat transfer device, which is employed for whole body cooling and is disposed in the venous vasculature, is disclosed in U.S. application Ser. No. 09/373,112, also incorporated by reference in its entirety.
While the previously mentioned techniques provide significant thermal control, they require the insertion of a catheter into the vascular system to induce heat transfer between the catheter and the blood stream. This is a relatively invasive procedure, which has an associated level of risk.
Accordingly, it would be desirable to provide an effective, less invasive method and apparatus for heating or cooling all or part of a patient""s body. It would also be desirable to provide an effective, less invasive method and apparatus for heating or cooling all or part of a patient""s body that could be employed in emergency situations, such as on an ambulance.
The present invention provides a method and apparatus for heating or cooling at least a selected portion of a patient""s body. The method begins by inserting a catheter through the urethra and into the bladder of the patient. A heated or chilled fluid is conducted through a supply lumen of the catheter and into the bladder. The fluid is evacuated from the bladder through a return lumen of the catheter. Finally, a quantity of urine is monitored which flows out of the bladder and through the return lumen of the catheter.
In accordance with one aspect of the invention, the rate of fluid flowing through the supply lumen of the catheter is adjusted in a manner that is based at least in part on the monitored quantity of urine flowing out of the bladder.
In accordance with another aspect of the invention, the fluid is conducted into the supply lumen at a substantially constant flow rate, or alternatively, at a periodically interrupted rate. In one particular embodiment of the invention, the flow rate is less than a flow rate that would substantially prevent fluid from flowing from the kidneys to the bladder. In this or another embodiment of the invention, the flow rate of fluid conducted into the supply lumen is substantially equal to a flow rate of fluid being evacuated from the bladder.
In accordance with another aspect of the invention, the pressure of the fluid flowing into the supply lumen is monitored. The pressure of the fluid flowing through the return lumen may be monitored as well.
In accordance with yet another aspect of the invention, a temperature differential is monitored between the fluid conducted into the supply lumen and the fluid flowing through the return lumen.